System for eliminating electrostatic cross-coupling effects



,ze Z4 0. Endzg I N l/E N TORS TTORNE Y l. 5E. GROSDOFF ErAL Filed Aprii 29, 195s .fz/f

SYSTEM FOR ELIMINATIZNIG ELECTROSTATIC CROSS-COUPLING EFFECTS July 10, 1956 6477/1/6 PSE SOURCE United States Patent() SYSTEM FOR ELIMINATIN G ELECTROSTATIC CROSS-COUPLING EFFECTS Igor E. Grosdoii, Princeton, and Richard 0. Endres, Moorestown, N. J., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Air Force Application April 29, 1953, Serial No. 351,920

Claims. (Cl. 178-69) This invention relates to electronic apparatus carrying discontinuous signals, and more particularly to the elimination of eects of electrostatic cross-coupling between electrical conductors in such apparatus.

It is sometimes necessary to juxtapose mechanically a plurality of electrically-conductive surfaces. If the surfaces are not shielded from each other, they are electrostatically cross-coupled, so that voltage signals on one of the surfaces may aect the voltage levels on others of the surfaces.

One place in which this capacitive coupling between conductors arises is in a storage tube of the type described in The selective electrostatic storage tube by J. Rajchman, RCA Review, March 1951, pages 53-97. In that storage tube, electron emission is controlled by the voltage levels on two orthogonal sets of spaced parallel bars or wires. When the control voltages on two orthogonal pairs of wires are at one level, electron emission passes through the window formed by those four wires; when the control voltages are at another level, the electron emission is suppressed. These wires are necessarily capacitively coupled. Consequently, when control voltages are applied to one wire in the form of voltage impulses, adjacent wires which are not pulsed and should not change in voltage, nevertheless, have impulses produced on them through the capacitive coupling.

Accordingly, it is an object of this invention to provide a novel system for eliminating the effects of electrostatic cross-coupling between a plurality of conductors.

Another object of this invention is to provide simple apparatus for a plurality of electrostatically cross-coupled surfaces to eliminate impulses that appear on one surface when voltage impulses are applied to another surface.

Still another object of this invention is to provide a new and simple system and apparatus for maintaining one conductor at a predetermined voltage level when voltage impulses are applied to another conductor which is electrostaticaly cross-coupled to the lirst.

These and other objects of this invention are achieved in an embodiment incorporating a pulse amplifier circuit of the type described in the U. S. patent to Igor E. Grosdoi, No. 2,628,290, issued on February l0, 1953. This circuit is made up of two pentodes connected in series, and it applies pulses to an output conductor connected to the junction of the tubes. In an arrangement of a plurality of these pulse ampliiier circuits, the plurality of output conductors attendant therewith are electrostatically cross-coupled. Thus, if a square-wave pulse is applied to a first one of the conductors, by its ampliiier circuit, and and a second one of the conductors is not pulsed, differentiated pulses appear on the second conductor through the capacitive coupling. To eliminate one of the vdilerentiated pulses, one of the tubes of the amplitier circuit for the second conductor is rendered conductive to provide a low-impedance path for that pulse. This tube is rendered conductive upon the operation of the amplifier circuit for the first conductor. The other of the diierentiated pulses is eliminated by a clamping diode connected ICC between the second conductor and a reference potential level. A duplicate arrangement is provided for eliminating the diiierentiated pulses that apepar on the first conductor when the second conductor is pulsed by its amplifier circuit.

The novel features of this invention, both as to its organization and mode of operation, may be better understood from reading the following description, together with the accompanying drawing.

Shown in the drawing are a lirst and second electrical conductor 2A, 2B which are unshielded and mechanically mounted adjacent each other so that they are electrostatically coupled. The resulting capacitance 4 between the two conductors is shown in broken lines. Pulses are applied to each conductor 2A, 2B by means of an amplifier 6A, 6B. The pulse amplifier circuit is of the type described in the patent cited above. Each amplifier 6A, 6B is made up of a first and second pentode SA, 8B, 18A, 19B connected in series. The cathode of the first tube 3A, 8B is connected to the anode of the second tube 19A, 10B and also through a resistor to the screen grid of the second tube 10A, 1GB. The control grid of the first tube 8A, 8B is connected to the screen grid of the second tube. The anode of the tirst tube 8, 8B is connected to a reference potential level or ground. A negative potential Biis applied to the cathode of the second tube. Each amplifier 6A, 6B is driven by a driver tube 12A, 12B whose anode is connected to the control grid of the second tube 16A, 16B and also through a load resistor 14A, 14B to ground. A negative potential B2- is applied to the cathode of the driver tube 12A, 12B, and the control grid of the driver tube is connected to the cathode of that tube through a grid resistor 15A, 15B.

rl`he operation of the driver tubes for the first and second amplifier circuits is in accordance with the condition of a trigger circuit 16 of the bistable multivibrator type. The trigger circuit 16 shown is a well known Eccles- Jordan circuit in which a pair of tubes have their anodes and control grids cross-coupled. This circuit has two stable conditions and it produces two output potentials, one high and one low, depending upon which tube is made conducting. The outputs 13A, 18B of the trigger circuit 16 are coupled to the-driver tubes through separate gating tubes 20A, 26B which afford a time control of circuit operation. The outputs 13A, 18B of the trigger circuit are connected respectively to the first of the control grids of each ofthe gating tubes 20A, 26B, and gating pulses are applied from an appropriate pulse source 22 to the second control grids of the gating tubes 20A, 29B in parallel through a capacitor 24. The anode of each gating tube 26A, 20B is connected to the control grid of the associated driver tube 12A,'12B, and also through the gridresistor 15A, 15B to the second negative potential level B2-. A third negative potential level B3- is applied to the cathodes of the gating tubes 20A, 20B, a fourth and a fifth potential level B4- and B5- respectively provide the negative bias for the second control grids of the gating tube and the grids of the trigger circuit tubes, and the second and third negative potential levels Bzand Bsare applied across the trigger circuit tubes.

The operation of the circuit described thus far is as follows: In the absence of a gating pulse, the driver tubes 12A, 12B are at zero bias and conducting so that their anodes are at a low potential level, and the second pentodes 10A, 10B of the amplier circuits are cut ott. Thus, there is no current iiowing in either series arrangement of the two pentodes 8A, 10A, 8B, 10B and both output conductors 2A, 2B are at ground potential. One or the other of the amplifier circuits 6A, 6B is operated with the application of a gating pulse depending upon the conditionrof the trigger circuit 16. Assuming the left tube of the trigger circuit is conducting and the right tube is cut od, then the first control grid of the first gating tube 20A is high with respect tothe cathode potential Briand the tube conducts with the application of a positive gating pulse. When the first gating tube 20A conducts, the control grid of the driver tube 12A goes negative cutting the driver tube 12A oft". Thus, a large positive pulse is applied to the control grid of the second pentode A of the first amplifier and it conducts causing the potential at the first conductor 2A to drop sharply. As screen current is drawn through the second pentode ltr/t., the volta ge at the control grid of the rst pentode 8A drops so that the first pentode is at least partly cut off. Upon termination of the gating pulse, the operation reverses itself as the driver tube lZA is restored to its normal conductive state cutting off the second pentode tube lA. The first pentode SA then starts to conduct heavily restoring the rst output conductor 2A to ground potential. Thus, a negative output pulse 26 appears on the first output conductor 2A.

Since the first control grid of the second gating tube 243B is at the low output potential of the trigger circuit i6, the tube B is not rendered conductive by the gating pulse, and the second amplifier 6B is not operated at this time. However, due to the capacitive couplingV 4 between the first and second output conductors, the second output conductor is not maintained at ground potential; but, instead dilierentiated pulses 28 (shown with broken lines) appear on the second output conductor 2B. In a similar manner when the trigger circuit condition is reversed, a gating pulse causes the operation of the second amplifier circuit 6B so that a negative output pulse is produced on the secondoutput conductor 2B and differentiated pulses appear on the first output conductor 2A through the capacitive coupling 4.

ln order to eliminate the positive going swing of the dierentiated cross-talk voltages 28, a first and second triode 30A, 30B are provided with the anodes respectively connected to the first and second conductors 2A, 2B and the cathodes connected to ground. The control grids of these triodesy are connected to their anodes to provide diodes of large current capacity. By means of these diodes 39A, 30B, the first and second output conductors 2A, 2B are clamped to ground so far as positive-going pulses are concerned.

In order to eliminate the negative swing of the crosstalk voltages 28, a first and second cathode follower 32A, 32B are respectively connected to the first and second amplifiers 6A, 6B. The cathode of each cathode follower 32A, 32B is connected Vto the screen grid of the associated first pentode tube 8A, 8B. The cathode resistors 34A, 34B are connectedto ground. The anodes of the cathode followers are connected to the positive side of a source of operating potential B+, and their control grids are negatively biased to cutoj potential,V and, also, respectively coupled through capacitors 36A, 36B to the anodes of the second and first driver tubes 12B, 12A.

The operation is as follows: When the first driver tube lZA is cut od and the first amplilier'circuit 6A operated, the positive going pulse at the anode of the first driver tube 12A is also applied to the second cathode follower 32B. The voltage at the cathode of the tube 32B rises, so that the voltage at the screen of the first pentode 8B in the second amplifier 6B also rises. This causes screen current to flow in the first pentode 8B reducing the impedance of that tube and, thereby, likewise reducing the impedance of the second output conductor 2B. Consequently, the negative cross-talk voltage which appeared on the second output conductor is eliminated or reduced to tolerable limits. Similarly, when the trigger circuit 16 is in the opposite state, and the second amplifier 6B is operated to produceV a negative output pulse on the second conductor 2B, a positive pulse is applied to the control grid of the VfirstY cathode follower 32A. Thus, lthere is an increase in voltage at the screen grid Vof the first pentode tube SA of the first amplifier 6A causing screen current to flow. Accordingly, a low impedance path is provided for the negative cross-talk voltage on the first output conductor 2A.

in the absence of a gating pulse, neither one of the amplifiers 6A, 6B are operated, and, correspondingly, the cathode followers 32A, 32B remain cutol so that both output conductors 2A, 2B remain electrically flat. The circuit has beenrdescrib'ed with either one or the other, but not both, of the amplifier circuits 6A, 6B being operate-fi, in accordance with the triggericircuit 16 being in te or the other of two possible states. The invention, of course, is not restricted to any particular system for determining the operation of the amplifierV circuits 6A, 6B. In other arrangements than that shown, both amplitier circuits might be operated at the same time. Y Under such circumstances, logic circuitry may be provided to keep both cathode followers 32A, 32B cut of at that time. An alternative system is made possible by the fact that an increase in voltage at the screens of the rst pentodes during the plateau of the pulse does not affect the output-pulse waveshape materially, because the control grids of the pentodes are held Vnegative during this time. Therefore, when both amplifiers are operated, both cathode followers may be pulsed without adverse effects.

This invention is not limited in its application to an arrangement involving two capacitively-coupled conduct-ors. It may also be applied to an arrangement in which several conductors are capacitively coupled. Under such circumstances, an alternative system for rendering the cathode followers conductive may be used: The control. grids ofthe cathode followers are all connected in parallel and capacitively coupled to the pulse source or otherwise connected to receive a positive pulse when one or more amplifiers are operated. Thus, when one or more of the amplifier circuits areY driven, allof the cathode followers are pulsed at the same time. As a result, the negative cross-talk voltage is eliminated from all the output conductors which are to remain at reference potential and there is no material effect on the signals on the output conductors which receive negative output pulses.

lt is seen from the above description of this invention that a simple, reliable and relatively economical system is provided for eliminating cross-talk effects of capacitively coupled conductors that have voltage pulse applied to them.

What is claimed is:

1. Electronic apparatus comprising a first and a second conductor electrostatically cross-coupled to each other, an electronic circuit operable for applying voltage impulses to said first conductonand means for eliminating resulting differentiated pulses on said second conductor by substantially maintaining said second conductor at a reference potential level comprising means providing a low impedance Vcurrent path to said second conductor upon operation of said electronic circuit including an electron control device having a plurality of electrodes, one of said electrodes being connected to said second conductor, and means for causing said electron control device to conduct responsive to operation of said electronic circuit.

2. Electronic apparatus as recited in claim l wherein said means .for maintaining said second conductor at 4a reference potential level further comprises diode means having one electrode connected to said second conductor and another electrode vat said reference potential level, said electron control device and said diode being connected to pass differentiated pulses of opposite polarities respectively.

3. Electronic apparatus as recited in claim l wherein said means for causing said electron control device to conduct includes means for increasing lthe potential of another one of said plurality of electrodes.

4. Electronic apparatus asrecited Vin claim 3 wherein said electron control device is an electron discharge tube having anode, cathode, control grid and screen grid electrodes, said cathode is connected to said control grid and to said second conductor, and said another one of said electrodes is said screen grid which is connected to said means for increasing the potential thereat.

5. Electronic apparatus as recited in claim 4 wherein said anode of said electron discharge tube is at said reference potential level, and said means for increasing the potential at said screen grid includes another electron discharge tube having anode, cathode and control grid trodes, and a resistor having one end connected to said screen grid and to the cathode of said another tube and the other end at said reference potential level.

6. In electronic apparatus wherein a irst and a second conductor are electrostatically cross-coupled to each other, and an electronic circuit operates to apply to said iii-st conductor voltage impulses of one polarity with respect to a reference potential level, the combination therewith of means for eliminating resulting diterentiated pulses on said second conductor by substantially maintaining said second conductor at said reference potential comprising means responsive to initiation of operation of said electronic circuit for providing a low impedance current path for impulses of said one polarity produced on said second conductor including an electron discharge tube having a plurality of electrodes, one of said electrodes being connected to said second conductor, and means for applying to another of said electrodes a potential of polarity opposite to said one polarity, at substantially the same time said impulses are applied to said second conductor and in response thereto.

7. Electronic apparatus as recited in claim 6 wherein said means for maintaining said second conductor at said reference potential further comprises means providing a low impedance current path for impulses of opposite polarity produced on said second conductorviucluding diode means having one electrode connected to said second conductor and another electrode at said reference potential.

8. in electronic apparatus wherein a rst and a second conductor are capacitively coupled whereby upon the application of voltage impulses to one of said conductors impulses appear on the other of said conductors, the combination therewith of means for eliminating impulses appearing on said first and second conductors due to said capacitive coupling comprising a first and second electron discharge tube each having one electrode respectively connected to said rst and second conductors, and rst and elecsecond means for respectively controlling the impedance of said first and second tubes responsive respectively to the application of voltage impulses to said second and first conductors, said first and second impedance-controlling means respectively including a third and fourth grid-controlled electron discharge tube each having another electrode respectively connected to another electrode oiz said first and second tubes.

9. In electronic apparatus wherein a first and a seco-nd conductor are electrostatically cross-coupled, and a iirst and a second electronic circuit respectively operated to apply voltage impulses to said iirst and second conductors and respectively include a first and a second electron discharge tube each having a plurality of electrodes, one electrode of said rst and second electron discharge tubes being respectively connected to said irst and second conductors; the combination therewith of means for eliminating impulses produced on one of said conductors by the application of voltage impulses to the other of said conductors including iirsf and second means for respectively reducing the impedance of said first and second electron discharge tubes responsive respectively to the operation of said second and rst electronic circuits, said rst and second impedance-reducing means being respectively coupled to another electrode of said rst and second electron discharge tubes.

10. Electronic apparatus as recited in claim 9 wherein said iirst and second electron discharge tubes each have anode, cathode, control grid and screen grid electrodes, said cathodes are respectively connected to said tirst and second conductors, said anode is at a reference potential level, said irst and second means for respectively reducing the impedance of said first and second electron discharge tube each include another electron discharge tube having anode, cathode and control grid electrodes, and a resistor having one end connected to the cathode of said another tube and to the screen grid of the associated one of said iirst and second tubes and the other end at said reference potential level, and said means for eliminating impulses produced on one of said conductors by the application of voltage impulses to the other of said conductors further includes first and second diodes each having one electrode respectively connected to the rst and second conductors and the other electrode at said reference potential level.

References Cited in the tile of this patent UNITED STATES PATENTS 2,439,651 Dome Apr. 13, 1948 

